Gas-cutting torch arrangement

ABSTRACT

In making sheet metal parts by means of oxygen cutting, the cutting torch is positioned so as to direct the oxygen jet at an angle of 4°-5° from the vertical in the direction of the cut and at an equal angle toward the part being cut out. An arrangement for orientating the gas cutting torch comprises two coaxial cylinders. The outer cylinder is mounted rotatably in relation to the inner cylinder. The inner cylinder is fixedly mounted on the carriage of the gas cutting machine and is connected through a flexible means to the cutting torch which is fitted in a bearing whose outer race is linked to the outer cylinder and is adapted to have an angular motion in a vertical plane. Gas supply hoses pass through the inner cylinder to the cutting torch.

This application is a divisional application of Ser. No. 463,063; filedApr. 22, 1974, now U.S. Pat. No. 3,944,441 of Mar. 16, 1976.

The present invention relates to the cutting out parts of various shapesfrom sheet metal by means of an oxygen jet, and more particularly to anarrangement for orientating the torch of a photo-tracing orprogramme-controlled gas cutting machine.

It is widely known to cut parts from sheet metal by means of an oxygenjet directed perpendicular to the plane of the metal sheet during thecutting movement of the torch.

With this method, a considerable amount of unburnt metal and its oxides,referred to as dross, becomes deposited on the bottom edges of the cutout parts.

To reduce dross, use is made of very pure (up to 99.9 percent) oxygenwhich promotes deoxidation of the metal during the cutting process.However, the production of very pure oxygen either results in reductionof the oxygen output or involves large expenses.

It is also known to reduce dross by decreasing the intensity of themetal heating flame, which entails reduction of the cutting rate. Inthis way the oxygen jet acts on the heated area of the metal for alonger time, bringing about better deoxidation.

Another method known in the art is to position the cutting torch overthe metal so that the oxygen jet is inclined 30°-50° from the verticalin the cutting direction and 15°-20° from the vertical toward the partbeing cut out. During the cutting movement of the torch the latter iskept in such a position as to maintain the oxygen jet at a constantangle to the cutting path irrespective of changes in the direction ofcut.

While applying an oxygen jet inclined 30°-50° from the vertical in thecutting direction and 15°-20° toward the part being cut out, thedistance between the end of the cutting torch and the surface of themetal must be maintained strictly constant. Any alternation of thisdistance affects the truth of the dimensions of the part concerned dueto dislocation of the point of intersection of the oxygen jet axis andthe surface of the metal. Moreover, the application of an oxygen jetinclined at the angles mentioned above appreciably bevels the edges ofthe parts produced.

There are known gas cutting machines for making parts from sheet metalby means of an oxygen jet.

Such machines comprise a carriage which mounts a cutting torchorientating arrangement, i.e. an arrangement which permits of settingthe cutting torch in a position where the oxygen jet is inclined at therequired angle to the plane of the metal sheet and enables the torch tobe kept in such a position as to maintain the oxygen jet at a constantangle to the cutting path irrespective of changes in the direction ofthe cut.

The cutting torch orientating arrangements known in the art comprise abracket to mount the torch, supply lines to deliver oxygen andcombustible gas to the torch and a drive mechanism arranged to rotatethe bracket with the torch and mounted on the carriage.

The gas supply lines in that arrangements are made in two embodiments,viz: (1) a system of hoses connecting the cutting torch direct to thegas supply; (2) a system of hoses connecting the cutting torch the gassupply through distributing manifolds.

In the first embodiment, the cutting torch can be rotated about its axisthrough an angle limited to within 3 π - 4 π because of the hosesbecoming twisted due to the rotational movement of the torch.

In the second embodiment, the construction is complicated and notsufficiently reliable since the distributing manifolds involved cannotensure proper gas tightness.

It is an object of this invention to provide an arrangement fororientating the gas cutting machine torch during the cutting process,which arrangement enables the cutting torch to rotate without twistingthe gas supply hoses and also precludes gas leakage in the working zone,thereby ensuring high operating reliability.

According to the invention, the cutting torch is positioned so that theaxis of the oxygen jet is inclined at an angle of 4°-5° from thevertical in the direction of the cut and at an equal angle toward thepart being cut out. The arrangement for orientating the cutting machinetorch comprises two coaxial cylinders. The inner cylinder is fixedlymounted on the carriage of the gas cutting machine. The outer cylinderis rotatably mounted on the carriage in relation to the inner cylinder.The latter is connected through a flexible means to the cutting torchwhich is fitted in a bearing. The outer race of this bearing is linkedto the rotatably mounted outer cylinder and is adapted to have anangular motion in a vertical plane. The hoses which supply gas to thecutting torch pass through the inner cylinder.

The invention consists essentially in the following. It is known thatthe inclination of the oxygen jet from the vertical in the direction ofthe cut and the consequent inclination of the heating flame make itpossible to cut metal at a high rate (up to 900 mm/min, depending on thethickness of the metal involved) by virtue of the inclined flame heatingthe metal layers ahead of it. Also, with the oxygen jet in thisposition, dross forming on the bottom edge of the cut is blown out bythe jet in the direction of the cutting movement and is thus preventedfrom depositing in the cut. This materially reduces dross on the edgesof cut-out parts. If the oxygen jet is inclined toward the part beingcut out, dross is deposited by the jet on the edge of the waste metal,the deposit of dross on the part edges being materially reduced. Whenthe oxygen jet is inclined from the vertical both in the direction ofthe cut and toward the part being cut out, the edges of the cut-outparts are free from dross.

By considering this it has been found that the truth of parts dimensionsand the amount of the edge bevel produced in gas cutting machines dependon the inclination of the oxygen jet. The larger the angle ofinclination, the less accurate are the dimensions of the parts and thelarger is the bevel of the edges. The slightest variation in thedistance between the torch end and the metal surface due thermaldistortion of the metal affects the truth of the dimensions.

We have found the minimum oxygen jet angles which provide fordimensional accuracy and reduction of the edge bevel. The minimuminclination of the oxygen jet from the vertical in the direction of thecut is 4°-5°. The minimum inclination of the oxygen jet from thevertical toward the part being cut out is also 4°-5°.

When the cutting torch is set so that the oxygen jet is inclined 4°-5°from the vertical in the direction of the cut, the metal is heatedsufficiently for the cutting to be done at a high speed. Increasing theangle of inclination does not produce an appreciable improvement of thecutting efficiency.

Inclining the oxygen jet at an angle of 4°-5° toward the part being cutout confines dross to the edge of the waste metal. Increasing this angledoes not improve the quality of the edge. Thus, the inclination of theoxygen jet at an angle of 4°-5° from the vertical in the direction ofthe cut and at the same angle from the vertical toward the part beingcut out gives the optimum conditions for high-speed cutting andobviation of dross. These conditions provide for a sufficiently highdimensional accuracy of parts cut out within the practical limits ofvariation in the distance between the end of the cutting torch and thesurface of the metal.

In producing parts of intricate form in a gas cutting machine by meansof an oxygen jet inclined to the plane of the metal sheet, the cuttingtorch has to be orientated by provision of an appropriate arrangement.

The arrangement provided by the present invention keeps the cuttingtorch orientated so that the angle of the oxygen jet to the cutting pathremains constant irrespective of changes in the direction of the cut.

This arrangement has an advantage in that the cutting torch does notrotate about its axis in being orientated, whereby twisting of the gassupply hoses is obviated, making it possible to dispense with gasdistributing manifolds.

The cutting torch does not have to rotate about its axis because it isconnected through a flexible means to the fixedly mounted inner cylinderand is fitted in a bearing whose outer race is linked to the rotatablymounted outer cylinder.

The cutting torch is adapted to have an angular motion in a verticalplane and can therefore be inclined at the required angles from thevertical.

The gas supply hoses are accommodated inside the fixedly mounted innercylinder to enable the bearing outer race to be rigidly linked to therotatably mounted outer cylinder. The element which links the bearingrace to the cylinder remains well clear of the gas supply hoses with theouter cylinder rotated through any angle. By directing the cutting torchto the gas supply direct through the hoses gas leakage in the workingzone is obviated.

Now the invention will be described in detail with reference to theaccompanying drawings in which:

FIG. 1 shows the positional relationship of the cutting torch and themetal sheet during the cutting process.

FIG. 2 diagrammatically shows the cutting process.

FIG. 3 is a partially cut-away front view of the cutting torchorientating arrangement.

FIG. 4 is a circuit diagram of a system for controlling the cuttingtorch orientating arrangement.

A part of intricate form is to be cut out from a carbon steel sheet 5 mmthick. A cutting torch 1 (FIG. 1) is positioned over a metal sheet 2 sothat the axis 3 of the oxygen jet is inclined at an angle α_(t) = 4°-5°from a vertical line 4 in the direction of a cutting path 5 and at anangle α_(n) = 4°-5° toward the part 6 (FIG. 2) being cut out.

The cutting torch setting for effecting the method according to theinvention is described somewhat later.

After the metal is burnt through at the point A, the cutting torch ismoved along the cutting path 5 at a constant speed V. During the cuttingprocess the position of the cutting torch is kept orientated so that theoxygen jet angles α_(t) and α_(n) remain constant irrespective of thedirection of the cutting path. Under these conditions the projection Qof the oxygen jet portion 7 cutting through the metal and the angle βbetween this projection and the tangent 8 to the cutting path at anygiven point B remain constant.

The process is continued until the cutting torch returns to the initialpoint A.

The edges of the part cut out in this manner are bevelled not more than3°. The dimensions of the part are accurate to within ±1 mm.

The arrangement shown in FIG. 3 comprises a cutting torch 1 and twocoaxial cylinders 10 and 11. The cutting torch 1 is mounted on a bracket9. The inner cylinder 11 is fixedly mounted on a carriage 12. The outercylinder 10 is mounted rotatably in relation to the inner cylinder 11.Gas supply hoses 13 pass through the interior of the fixedly mountedcylinder 11 and are connected to the cutting torch 1. A flexible shaft14 connects the cylinder 11 to the cutting torch 1.

The cutting torch 1 is fitted in a bearing 15. The outer race 16 of thebearing 15 is linked to the rotatably mounted cylinder 10 by a bracket9. The cylinder 10 has a toothed rim 17 arranged to mesh with areduction gear 18 which is mounted on the carriage 12. The reductiongear 18 is connected to a servomotor 19 and a feedback pickup 20.

The output of the pickup 20 is connected to the input of a comparisonelement 21 (FIG. 4). The other input of the comparison element 21 isconnected to a photo-tracing control system 22. The output of thecomparison element 21 is connected to the servomotor 19 through anamplifier 23.

When it is required to set the cutting torch at the angle α_(t) in thedirection of the cutting path, and at the angle α_(n) towards the partbeing cut out, it is necessary to proceed as follows:

a. Insert the tip with a needle to replace the nozzle, the length of thetip being equal to the total length of the nozzle and to the distancebetween the tip and the surface of the sheet metal that is kept constantduring cutting.

b. Then one sets the cutting torch 1 with the outer race 16 at an angleof α=α_(t) √2 along the radial groove of the segment 24, the radius Rhaving a calibration.

c. Subsequently energize the system and pre-set the movement of theneedle along a straight line, e.g. along one of the actuatorcoordinates.

d. Next turn the bracket 9 together with the segment 24 about the axisof the coaxially mounted cylinders 10, 11 at an angle β = 40° - 50°towards the part being cut. Setting this angle according to the selectedline is effected in a plane extending across the segment 24 parallelwith the projection of the oxygen jet on the surface of the sheet metal.Then the bracket 9 is secured to the outer cylinder 10 by means of anysuitable fastener.

When a change in the direction of the cut occurs, the error voltage U₁produced by the element 21 by comparing the voltage U₂ supplied by thecontrol system 22 with the voltage U₃ supplied by the feedback pickup 20is fed through the amplifier 23 to the servomotor 19. Thus actuated, theservomotor 19 drives the reduction gear 18 and thereby rotates the outercylinder 10 with the bracket 9 and the feedback pickup 20 until there isno more error voltage. Thus the angle is restored, and thereby theangles α_(t) and K_(n) are automatically maintained at constant values.

As can be seen from the description given herein, the invention improvesthe dimensional accuracy of the cutting process and decreases the bevelof the cut edges. The cutting torch orientating arrangement enables thecutting torch to be rotated without twisting the gas supply hoses,obviating gas leakage in the working zone.

What is claimed is:
 1. An arrangement for orientating a torch for gascutting machine, in making parts from sheet metal by means of oxygencutting, the arrangement comprising a carriage in the cutting machinefor mounting a cutting torch and two coaxial cylinders, the innercylinder being fixedly mounted on said carriage while the outer cylinderis rotatably mounted in relation to said inner cylinder, which isconnected through flexible means to said torch; the axis of the latterintersecting that of said cylinders at a point that lies on the surfaceof the sheet metal; said torch being fitted in a bearing which has anouter race linked to said outer cylinder; means to impart an angularmotion to said torch in a vertical plane, at a predetermined small anglefrom the vertical, the angle of the oxygen jet to the cutting pathremaining substantially constant irrespective of changes in thedirection of the cut; gas-supply hoses, passing to said torch throughsaid inner cylinder; and means for eliminating twisting of said hoses,constituted by said fixed inner cylinder, said flexible means and saidbearing.